Earth Rod Readings

[1st Solar]

Hi, my first post so be gentle.
Got my MCS inspection on the 24th March and I'm struggling with earthing the array frame.
I have installed an SMA 4000tl inverter on a PME system, and not being galvanically separated I have placed the required earth rod (my first ever in many years of sparking!) adjacent to the system connected using 10mm csa earth wire to strategic points on the support frame.

The question is' using my Megger 1553, how do I test this earthing arrangement and what readings are allowed for DC circuits?
Should I test it similar A.C. TT system ie: RCD is 30ma so 50v/30ma = max 1666 ohms
(or should I be aiming for under 100 ohms as recommended on other posts on this site), is it different (earth path wise) when reliant on a DC circuit to create the fault current?.
Confused!

Thanks in anticipation

 

[yellowvanman]

Unless you have the earth rod testing options the only other way to test the stake is by doing your standard Zs test, using the stake as your earth connection.

As for what would be a good value, BS7671 states earth stakes should be less that 200 ohms (for stability) whilst the NICEIC say aim for 100 ohms. If I got less than 200 that'll do for me! Unless your unlucky with soil conditions etc. getting less than 200m should be straightforward.

 

[BruceB]

Aim for less than 100 at this time of year and it should always be less than 200.

Regards
Bruce

 

[GreggElectrical]

You are right 1st solar. BS7671 states the maximum Zs for a 30ma rcd is 1667 ohms. Still, as pointed out by my NICEIC inspector one time, would you accept a reading above 200? if not then you have your answer.